The present invention relates to a hydraulic control system for automatic transmissions.
Generally, a conventional automatic transmission used in vehicles includes a torque converter, a multi-stage shift gear mechanism connected to the torque converter, and a plurality of friction members, which are actuated by hydraulic pressure, for selecting one of the gear stages of the shift gear mechanism.
A hydraulic control system for automatic transmissions used in vehicles operates by the selection of friction members using hydraulic pressure, created by the pumping of oil by a hydraulic pump, passing through a control valve. As a result, shifting can be realized automatically and appropriate to the driving state of the vehicle.
The above hydraulic control system is realized including pressure regulating means for regulating hydraulic pressure created in a hydraulic pump, manual and automatic shift control means for forming a shift mode, hydraulic pressure control means for controlling shift quality and shift response for the forming of a smooth shift mode during shifting, damper clutch control means for operation of a torque converter damper clutch, and hydraulic distribution means for dispersing an appropriate amount of hydraulic pressure to each of the friction members.
In the hydraulic control system structured as in the above, through the ON/OFF and duty control of solenoid valves by a transmission control unit (TCU), hydraulic distribution of the hydraulic distribution means is changed and friction members to be operated are selected, realizing the control of shift stages.
However, in the above hydraulic control system, as line pressure is controlled according to the operation of the damper clutch, precise control of line pressure is difficult when the damper clutch slips during beginning and middle points of shifting, and a problem arises wherein line pressure varies with the operation of the damper clutch.
Further, when controlling shifting from one shift stage to another, shift quality is greatly affected by how precise the timing is to release hydraulic pressure operating on one friction member and supply it to a new friction member.
Also, in the prior art hydraulic control system, engine rpms can quickly increase, the shift mechanism can become interlocked, and the engine can briefly change into a neutral state.
Designs are offered in the prior art in which shift-valve structure is changed to improve shift quality by controlling the timing supplying hydraulic pressure, but these changes result in the drawback of complicating shift valve structure.